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Time Zones

The predefined locations on this site will have the Time Zone set. For user-entered locations, choose a Time Zone from the drop-down on the custom page. To set the Time Zone in a link, see the FAQ entry.

Around the mid-19th or early-20th century, before the adoption of Standard Time zones, cities and towns used their own local time which was usually based on solar noon of their location. This caused major complications for the railroad companies when making arrival and departure timetables because each town had its own local time which was different from other nearby towns. To ease all the scheduling problems, they created time zones for large areas and set all the local times the same. They did this by making all the clocks in that area (the time zone) have their time offset from Greenwich Mean Time (GMT) be the same as all other towns and cities in the same time zone. The time offset was usually an hour multiple, e.g. +2:00 or -5:00, but a few areas use a fractional part of an hour, such as Newfoundland, Canada at -3:30 and Kathmandu, Nepal at +5:45. These time zones were later adjusted, officially named, and set into law—or adopted—by the government of the country. Most countries or regions have not changed their time offset since then, but many have.

A few smaller areas have chosen their own time offset and daylight saving time (DST) Rules that differ from the geographical or political division that they border or are contained in. For example, the state of Quintana Roo in Mexico has differed from their country and neighboring state’s time offset and DST observance a few times—in 2015 they moved their time offset to -5:00 and stopped observing Mexican DST.

Using the Time Zones defined on this page will allow the calendar to adjust for both Time Offsets and DST rules that vary over time. Our predefined locations, for applicable regions, will have this Time Zone set or you can choose it on the custom page. When a calendar is generated using a rule on this page, it will be shown along with the latitude and longitude information in the header, e.g. Time Zone: America/Cancun. (You must select the “Latitude, longitude and time info” checkbox to see this.)

Our DST page details the DST rules we use during calendar creation—this page documents the more complicated situations.

On this site, we consider GMT and UTC (Coordinated Universal Time) synonymous.



Time Zones Used While Creating the Calendars

The Time Zone rules have been researched using the IANA time zone tables, Wikipedia, newspaper or other published articles on the internet, or information from the country or city’s website. While there are many more zones defined in the IANA tables, use only the Times Zones listed on this page. Using Time Zones not on this page will be ignored by the code generating the calendar.

The future dates of the time offset and DST observance are set by the government of the country or locality and are subject to change. Also see FAQs and DST adjustments.

The rules on this page will supercede the basic DST rules documented on our DST rules page for all the years from the adoption of the time offset to the year 2099.

For corrections or to have a new time zone added, please contact us.

South Korea flag South Korea  

South Korea has changed its time offset between +9:00 and +8:30, and has used South Korea DST rules since 1948—note that the DST rules indicate it is not observed for the following years: 1952 to 1954, 1961 to 1986, and 1989 to the present.

Use Time Zone: Asia/Seoul
Area: Entire country

From To Offset DST Rule
1964 Aug 10 present +9:00 South Korea
1954 Mar 21 1964 Aug 9 +8:30 South Korea
1948 1954 Mar 20 +9:00 South Korea
1912 1947 +9:00 none
adoption 1911 +8:30 none

North Korea flag North Korea  

North Korea has never observed DST, but it has changed its time offset between +9:00 and +8:30.

Use Time Zone: Asia/Pyongyang
Area: Entire country

From To Offset DST Rule
2018 May 5 present +9:00 none
2015 Aug 15 2018 May 4 +8:30 none
1912 2015 Aug 14 +9:00 none
adoption 1911 +8:30 none

Mexico flag Mexico — Quintana Roo  

The Mexican state of Quintana Roo has changed its time offset between -6:00 and -5:00, and has both observed and not observed Mexican DST rules.

Use Time Zone: America/Cancun
Area: Entire state of Quintana Roo

Representative cities: Cancún, Chetumal, Playa del Carmen, San Miguel de Cozumel, Felipe Carrillo Puerto, Isla Mujeres, José María Morelos, Kantunilkín, Tulum, Bacalar, Puerto Morelos.

From To Offset DST Rule
2015 Feb 1 present -5:00 none
1998 Aug 3 2015 Jan 31 -6:00 Mexico
1981 Dec 23 1998 Aug 2 -5:00 Mexico
adoption 1981 Dec 22 -6:00 none

Mexico flag Mexico — Campeche & Yucatán  

The states of Campeche and Yucatán have changed their time offset between -6:00 and -5:00. They currently observe Mexican DST rules, but in the past they have not.

Use Time Zone: America/Merida
Area: Entire states of Campeche and Yucatán

Representative cities, in Campeche: Campeche, Ciudad del Carmen, Champotón, Escárcega, Calkiní; in Yucatán: Mérida, Tizimín, Valladolid, Umán, Kanasín, Progreso.

From To Offset DST Rule
1992 Dec 2 present -6:00 Mexico
1981 Dec 23 1992 Dec 1 -5:00 none
adoption 1981 Dec 22 -6:00 none

Bahamas flag Bahamas  

The Bahamas has always been in the Eastern (-5:00) time zone. From 1976 to the present, they matched the DST observance of the United States; from 1964 to 1975, they used their own DST rule.

Use Time Zone: America/Nassau
Area: Entire country

Representative cities/towns: Nassau, Freeport, Spanish Wells, Marsh Harbour, Georgetown, Freetown, Coopers Town, Andros Town, Clarence Town, Long Island, High Rock, West End

From To Offset DST Rule
1976 present -5:00 North America
1964 1975 -5:00 Bahamas
adoption 1963 -5:00 none

Turks and Caicos flag Turks & Caicos  

The British Overseas Territory of Turks and Caicos Islands has changed its time offset between -5:00 and -4:00, and has both observed and not observed DST.

Use Time Zone: America/Grand_Turk
Area: Entire territory

Representative cities/towns: Cockburn Town, Cockburn Harbour, Providenciales, Bottle Creek, Conch Bar, Big Ambergris Cay

From To Offset DST Rule
2018 Mar 11 present -5:00 North America
2015 Nov 1 2018 Mar 10 -4:00 none
1979 2015 Oct 31 -5:00 North America
adoption 1978 -5:00 none

São Tomé and Príncipe flag São Tomé and Príncipe  

São Tomé and Príncipe, for 2018 only, changed its time offset from 0:00 to +1:00. It has never observed DST.

Use Time Zone: Africa/Sao_Tome
Area: Entire country

Representative cities/towns: São Tomé, Santo António

From To Offset DST Rule
2019 Jan 1 present 0:00 none
2018 Jan 1 2018 Dec 31 +1:00 none
adoption 2017 Dec 31 0:00 none


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